The present invention relates to an apparatus for detecting deterioration of a catalyst disposed in an internal-combustion engine, and more particularly it relates to an apparatus for detecting deterioration of a catalyst based on an oxygen storage capacity of the catalyst.
As an example of techniques for detecting deterioration of a catalyst placed in an exhaust system and having oxygen storage capacity (OSC), Japanese Patent Application Publication No. H7-189780 discloses an apparatus for detecting deterioration of a catalyst by changing air-fuel ratio of exhaust gas in a certain cycle and monitoring the behavior of air-fuel ratio in the downstream side of the catalyst when air-fuel ratio of exhaust gas is changed in certain cycle.
Japanese Patent Application Publication No. H7-19033 discloses a technique for determining deterioration of a catalyst by measuring air-fuel ratios in the upstream and downstream sides of the catalyst by changing air-fuel ratio of exhaust gas from lean to rich or from rich to lean. Catalyst deterioration is determined based on time delays in alteration of the air-fuel ratio in the downstream side of the catalyst.
Japanese Patent Application Publication No. H7-151002 discloses a technique that uses various kinds of sensor information and a model representing an OSC of a normal catalyst to calculate an OSC of a current catalyst to determine deterioration of the current catalyst when the calculated OSC is less than a predetermined OSC.
In the technique discussed in the above-mentioned Publication No. H7-189780, air-fuel ratio of the exhaust gas needs be changed in a certain cycle, which may produce bad emission. Besides, according to the technique disclosed in the above-referenced Publication No. H7-19033, the catalyst deterioration must be determined based on instantaneous values. This would produce inaccurate detection due to dispersion of measurement capabilities of sensors, engine operating environments and so on. The technique disclosed in the above-referenced Publication No. H7-151002 is very complicated in the design of a model representing OSC of the normal catalyst, needing large sensor information for developing the model.
Thus, it is an objective of the present invention to provide a catalyst deterioration detecting scheme that is capable of accurately determining the catalyst deterioration.